1 Introduction: Cape Perpetua ROV Fish Survey Report
Data are not presented for ROV surveys at the Cape Perpetua Marine Reserve. Rather, the goal of this report is to introduce the available long-term ROV video dataset acquired and ongoing at the marine reserve, and to describe features that make the constraints and opportunities of this data distinct from those at the other reserves.
2 ROV Methods
Detailed methods documenting the survey design, field sampling methods, and video review methods for the Remotely Operated Vehicle (ROV) video sampling are presented in the ROV Methods Appendix. The following sections briefly summarize aspects of the ROV methods that are distinct for the Cape Perpetua Marine Reserve.
Remotely Operated Vehicle (ROV) video sampling is conducted in the Cape Perpetua Marine Reserve. There is no paired comparison area with suitable matching habitat characteristics for ROV sampling. The ROV sampling strategy for this marine reserve differs from the other reserves because of the distinct characteristics of the rocky reef at Cape Perpetua. The Cape Perpetua Marine Reserve features only a very limited distribution of rocky reef habitat, composed of numerous, discrete low-relief rock outcrops extending only a few meters off the relatively flat sandy and gravelly seafloor. The patches generally have a long, thin shape (up to hundreds of meters long and sometimes only 10 - 20 m wide), and a generally north-south orientation of the long axis. They lie at a consistent depth of 46 - 49 m in a region of relatively flat seafloor.
The limited habitat area broken into numerous distinct patches makes the sampling design of multiple transects distributed randomly within a large reef area impractical. Instead, the sampling design involves repeating transects in the same habitat patches over time. The ROV samples the same strip of rocky habitat on every site visit. Two multi-segment transect lines were drawn that maximize the interception of patches of rocky habitat, one approximately 1.6 km long and the other approximately 2.1 km long. On each ROV sampling day, one extended dive is conducted along each of these two lines. The direction of travel is chosen according to prevailing winds and currents.
First sampled by ROV in 2000, there is a long history of video observations from the same rocky patches (Table 1). Sampling the nearshore environment with ROVs first started in the late 1990’s with California Department of Fish and Game and then ODFW a few years later. This application of the tool was new at the time and standard methods did not exist for the sampling application. The first few years of sampling at Cape Perpetua were a time of method development, testing, and modification (e.g., Amend, et al. 2001; Fox, et al. 2004). ROV sampling of individual parts of these two lines began in 2000, but the consistent multi-patch lines originated around 2004.
Effects of hypoxia were first observed at Cape Perpetua in July 2002, and repeat sampling occurred in August and September of that year examining return of fish populations (Grantham, et al. 2004). In the summer of 2006 the region experienced a severe hypoxic episode (Chan, et al. 2008), and in response a project was initiated to conduct ROV sampling repeatedly through the summer season, documenting large-scale mortality events of benthic invertebrates as part of an externally-funded initiative. This project provided more repeated intra-season sampling efforts through 2011. During this period, there were equipment challenges including a transition from standard-definition to high-definition video and errors in the ROV tracking equipment that have delayed the creation of a consistent timeseries dataset of fish and invertebrate densities. Additional work on these issues is expected to yield a usable density timeseries.
Table 1 presents the complete ODFW ROV sampling history for the rocky habitat patches that comprise the current marine reserve:
The data from each of these dates may not be fully usable for the purposes of establishing a timeseries of species densities from the same rocky habitat patches, especially during the early method development years, but may contribute presence/absence, relative abundance, and community composition data. More work needs to be focused on applying consistent data filtering and aggregation procedures across the entire dataset. Unfortunately this intensive effort was not possible to complete for inclusion in this report. However, ODFW intends to continue investment in this dataset, both in terms of sampling over time and in analytical effort to establish a rigorous timeseries. This effort is expected to be of particular importance going forward in the context of assessing ocean change over time. A subset of the data are available for years 2015 - 2019. Data for these years have been processed to generate species-specific density estimates for all fish species observed, but no statistical analysis has yet been conducted to assess inter-annual trends. Data processing for calculating invertebrate densities for these years is not yet complete.
2.1 Survey Maps
2.1.1 Cape Perpetua Marine Reserve
Fig. 1: Map of ROV transects at the Cape Perpetua Marine Reserve
3 Discussion
The Cape Perpetua Marine Reserve plays a distinct role from the other marine reserves relative to the overall Marine Reserve Program’s mission. The very small size and distinct geomorphology of the reserve’s rocky reefs, the setting along the coastline in a broad region with very little other subtidal rocky habitat, and the oceanographic forcings (e.g. upwelling, retention/circulation of shelf waters, and resultant hypoxia) that contribute to highly dynamic fish and invertebrate communities are likely to generate distinct dynamics from the other marine reserves. Accordingly, the general conceptual model of monitoring fish populations over time with the goal of detecting slowly-accumulating changes in size structure and population density of resident fishes and invertebrates, may not be the most useful model to apply at the Cape Perpetua Marine Reserve. Instead, this reserve can serve as a site to focus on the goal of understanding the connections between oceanographic forcings and species’ population dynamics and habitat usage. The ability to re-sample the same transect in a single day with the ROV provides a unique opportunity relative to other reserves, where randomized sampling adds an additional element of stochasticity to the data.
Despite the exclusion of ROV data displays from this report, a few key observations may be useful to report. The most striking patterns observed in ROV data at the Cape Perpetua Marine reserve are the high variability in some individual fish species’ densities among sampling dates, and the sometimes very high densities seen, even among non-schooling demersal fish such as Lingcod. These observations support the conclusion that movement between the patch reefs comprising the marine reserve and other relatively distant rocky habitats likely plays a substantial role in shaping the fish density and community composition observed at any given time. One hypothesis consistent with these observations is that the high densities derive from an “island refuge effect”, a term applied from landscape ecology that describes the potential for imbalanced immigration and emigration on small, isolated habitat patches. With little nearby habitat to spread across, those moving individuals that eventually arrive at a small, isolated habitat patch may contribute to higher local densities. By contrast, the low densities sometimes observed may indicate a responsiveness to oceanographic conditions, hypothesized to represent an emigration of fish from the rocky patch reefs to distant coastal habitats, perhaps in response to the hypoxic episodes that are known to affect this area, or in response to other unknown cues.
4 Contributions from ROV surveys at Cape Perpetua
The ROV data generated at this site have been utilized in a number of important contributions to the understanding of nearshore systems off Oregon. The list below showcases prior uses of ROV video data from the rocky reefs at Cape Perpetua.
Publications:
Chan, F., Barth, J., Lubchenco, J., Kirincich, A., Weeks, H., Peterson, W., Menge, B. (2008). Emergence of anoxia in the California Current large marine ecosystem. Science 319: 920.
Grantham, B. A., Chan, F., Nielsen, K.J., Fox, D.S., Barth, J.A., Huyer, A., Lubchenco, J., Menge, B.A. (2004). Upwelling-driven nearshore hypoxia signals ecosystem and oceanographic changes in the northeast Pacific. Nature 429: 749-754.
Reports available at https://www.dfw.state.or.us/MRP/publications/index.asp#Habitat:
Amend, M., Fox, D.S., Romsos, C. (2001). 2001 Nearshore rocky reef assessment ROV Survey. Newport, OR: Oregon Department of Fish and Wildlife. 33 pp.
Fox, D.S., Merems, A., Amend, M., Weeks, H., Romsos, C., Appy, M. (2004). Comparative Characterization of Two Nearshore Rocky Reef Areas : A high-use recreational fishing reef vs. an unfished reef. Newport, OR: Oregon Department of Fish and Wildlife. 67 pp.
Weeks, H., Merems, A. (2004). 2003 Nearshore Rocky Reef Habitat and Fish Survey, and Multi-Year Summary. Final Report for 2003-04 Grant. Cooperative Agreement No. 001-3176C-Fish. Oregon Department of Fish and Wildlife. 13 pp.
Reports available on request:
Marion, S. (2016). Assessment of Nearshore Biogenic Habitat. Oregon State Wildlife Grant Program Final Project Report for grant F13AF00940. Oregon Department of Fish and Wildlife. 32 pp.
Marion, S. (2020). Abundance Estimation for Nearshore Groundfish from ROV Video Surveys of Oregon’s Nearshore Rocky Reefs. Report for Pacific Fishery Management Council, Science and Statistical Committee, ROV Methodology Review conducted in Santa Cruz CA, Feb. 2020. Oregon Department of Fish and Wildlife. 35 pp. with accompanying 350 MB HTML figure interface.